Allow USB notification to show when primary SD allows UMS and MTP

Previously if primary SD is set to allowMassStorage="true" the USB
dialog would never show.  This checks if persist.sys.usb.config is
set to mtp,adb and then allows the USB notification to show. With
this you can then have the option to select from MTP, PTP and Mass
storage when clicking the pull down notification. When Mass Storage
is selected it activates the USB connected dialog to turn on USB
storage. When set back to MTP the USB connected notification disappears.

Change-Id: I2287075ec93cae75f19e8fb59965d9dddb234aca
Merge pull request #79 from alteredlikeness/jb43-legacy-alt0

Allow USB notification to show when primary SD allows UMS and MTP